Heretofore, in the electrolysis of brine, a diaphragm method utilizing an electrolytic cell comprising an anode compartment and a cathode compartment separated from each other by a porous neutral diaphragm made of asbestos or the like has been used in place of the mercury method. This diaphragm method, however, has the disadvantage that high purity alkali metal hydroxide cannot be obtained. Thus, an ion exchange membrane method using a cation exchange membrane has been developed for the production of high purity alkali metal hydroxides.